A so-called polymer electrolyte fuel cell (Polymer Electrolyte Fuel Cell: hereinafter called “PEFC” as needed), has its operating temperature of from a room temperature to about 80° C. Also, since PEFC makes it possible to employ inexpensive general-purpose plastics, etc. for members constituting its fuel cell body, it is possible to realize reduction in weight. Furthermore, PEFC makes it possible to achieve thinning of a polymer electrolyte membrane, enabling an electric resistance to be reduced, thereby enabling a power loss to be reduced relatively easily. Due to PEFC having not a few advantages as described above, it is applicable to a fuel cell vehicle, a home cogeneration system, and the like.
As an electrode catalyst for PEFC, there has been proposed an electrode catalyst in which a platinum (Pt) or platinum (Pt) alloy, i.e., a component for the electrode catalyst, is supported on a carbon serving as a support (for example, MATSUOKA et al., “Degradation of Polymer Electrolyte fuel cells under the existence of anion species”, J. Power Sources, 2008.05.01, Vol. 179 No. 2, P. 560-565).
Conventionally, there have been disclosed that, as for an electrode catalyst for PEFC, if the content of chlorine contained in the electrode catalyst is 100 ppm or more, it is not desirable as an electrode catalyst (for example, Japanese Un-examined Patent Application Publication No. 2003-129102 (Japanese Patent No. 4,286,499)); and that this is because if the content of chlorine contained in the electrode catalyst is 100 ppm or more, it is impossible to obtain a sufficient catalytic activity for the electrode catalyst for fuel cells; and corrosion of its catalyst layer will occur, thus shortening the life of the fuel cell.
Then, there is disclosed, as the catalyst component of the electrode catalyst, a powder of platinum (Pt) or platinum (Pt) alloy that contains less than 100 ppm of chlorine (for example, Japanese Un-examined Patent Application Publication No. 2003-129102 (Japanese Patent No. 4,286,499)).
As for the preparation of a powder of the platinum (Pt) or platinum (Pt) alloy, there is disclosed the following method: forming a melt which contains a low-melting mixture of alkali-metal nitrate, a chlorine-free platinum compound and a chlorine-free compound of alloying elements; heating the melt up to a reaction temperature at which the platinum compound and the compound of the alloying elements are thermally decomposed to give an oxide; cooling the melt; and the melt is dissolved in water and the resulting oxide or mixed oxides are converted into a powder of platinum or platinum alloy by successive reduction.
Incidentally, the present applicant submits, as publications where the above-mentioned publicly-known inventions are described, the following publications: